Panel assemblies for solar collectors frequently comprise a flat carrier panel comprising heat-conductive material, one surface of which receives the solar radiation while disposed at the opposite surface thereof is a pipe arrangement which may be for example of a meander-like or serpentine configuration and through which flows a heat exchange fluid to be heated by the solar radiation impinging on the panel assembly. The carrier panel and the pipe arrangement should be joined together by as intimate a connection as possible in order to maximise the transfer of heat from the carrier panel to the pipe arrangement and thus to the heat exchange fluid flowing therein. On the other hand, an important consideration is that the cost of manufacturing such plate assemblies should be kept as low as possible, for obvious economic reasons.
With regard to the cost aspect, the use of pipe arrangements which are formed from pipes of round cross-section makes it easy to shape the pipe arrangement, using straight pipe sections and curved pipe sections which interconnect the straight sections. However, with pipes of round cross-section, the area of the contact between the pipe and the carrier panel is only small, so that the transfer of heat between the pipe and the carrier panel would be relatively slight, with such a configuration. For that reason, such an arrangement requires a large amount of a joining agent, for example solder or brazing material, to connect the carrier panel and the pipe arrangement together, in order to provide a large heat transfer area at that point. In that respect therefore, the operation of making the connection between the pipe and the carrier panel is not only time-consuming but also requires a large amount of material, all of which increases the costs of production. In addition, that design configuration does not necessarily ensure that gaps between the pipe and the carrier panel are uniformly and cleanly filled with the joining agent used, while in addition, there is no reliable guarantee that, when joining the components together, the carrier panel remains in its flat condition over substantially its entire extent, all those being factors which may count against a satisfactorily large surface area contact for heat transfer from the carrier panel to the pipe arrangement.
In a process for the production of a radiant heating element (see German published specification (DE-AS) No. 16 27 628), the wall portion of the pipe arrangement which is towards the carrier panel is brought into contact with a joining agent such as a bed of solder or brazing, and a filling material is introduced into the spaces defined between the pipe runs of the pipe arrangement. The thickness of the filling material introduced is greater than the diameter of the pipe which is of round cross-section. In the recess in the filling material, which corresponds to the configuration of the pipe arrangement, a cover layer is positioned over the pipe arrangement, in the form of a resilient cushion member which is adapted in respect of its shape to the pipe arrangement and which applies a pressure to the pipe arrangement on the carrier panel when the pipe is disposed in the recess, the intermediate assembly comprising the carrier panel, pipe arrangement, joining agent, filling material and above-mentioned cushion member then being clamped between pressure plates. In that process, both the filling material must have a recess which matches the layout of the pipe arrangement, and the resilient cushion member must also be of a corresponding form, while the cushion member has to be laid with precision into the recess in the filling material, so as to cover over the pipe runs, and that is a time-consuming and costly operation. Further problems are involved in regard to selecting a suitable material which can resist the soldering or brazing temperatures involved, for constituting the cushion member.
German laid-open application (DE-OS) No. 28 06 487 discloses a solar collector which is made up from two sheet metal plates, wherein suitable depressions or recesses are provided in the metal plates, to provide at least one conduit for carrying a heat exchange fluid, which extends in a meander-like configuration. In that assembly, the two plates must be subjected to a deep drawing or other impressing operation and must be precisely aligned relative to each other and disposed accurately one upon the other in order to form the meander conduit.
British patent specification No. 826 625 discloses a plate-type heat exchanger having D-shaped cross-section pipes. In that arrangement, the pipes of D-shaped cross-section have a flattened portion which bears against a carrier panel, while the top side of the pipes and the top side of the carrier panel are covered with a plate which is provided with grooves. The grooves are adapted in respect of their dimensions to the pipes used in that assembly. It will be appreciated that the grooved plate can only be manufactured at relatively high cost, and that has an adverse effect on the total price of a heat exchanger of that kind.